Extract driver code into engine.run()
* temple.py is now a simple runner for player
Make level loading private within engine module
Clean up Levels module
* Foreword is just introductory text, not a level
* Levels do not need name attributes
Extract foreword printing into new method
* Add pseudocode for game loop
* Remove vestigial Foreword() from level_dict
Reorganize engine.py
* Remove private/public comments
* Reverse _load_game_level() and _load_game_intro()
Remove redundant call on press_enter_to_continue
* Add missing parens